I have set the aspect ratio for nativeads as Portrait. but only video ads are coming in Full Screen Aspect ratio.. Image ads are still in Landscape

Question

NativeAdOptions nativeAdOptions = new NativeAdOptions.Builder().setMediaAspectRatio(MediaAspectRatio.PORTRAIT).build();
                builder = new AdLoader.Builder(context,my_unit_id).withNativeAdOptions(nativeAdOptions);

After doing this the image should come as Portrait. But only video ads are coming as portraits. Image ads are still coming without the following aspect ratio. Sometimes they come as Square, Some times they come as Portrait. Most of the time they come as Landscape.

Any solution will be highly helpful...